In recent years advances in high coercive metalized tape have stimulated research into magnetic heads which comprises high magnetic density core material. Promising materials for such magnetic cores can be found in Sendust (Tradename) and amorphous alloys. However, the method currently used in forming magnetic gaps in ferrite cores cannot readily be applied to the formation of magnetic gaps in such high magnetic density core materials. More specifically, in the current method use is made of glass which is sandwiched between ferrite core halves and bonded thereto by fusion at elevated temperatures. Advantages reside in the fact that in the fusion process the glass partially diffuses into the core material and increases the bonding strength and that a suitable glass material can be easily found to match the thermal expansion coefficient of the core material used. However, Sendust and amorphous alloys have a considerably low bonding strength to glass, and in addition the thermal expansion coefficient of Sendust is typically 170.times.10.sup.-7 which is considerably greater than that of glass that ranges between 50.times.10.sup.-7 and 120.times.10.sup.-7. Mismatch in thermal expansion coefficient presents a serious problem. The low bonding strength is considered to arise from the fact that glass is less capable of diffusing into such materials than it is with ferrite materials. In the case of amorphous alloys, the difficulty is that their crystalization temperature, which is around 500.degree. C., requires that glass fusion be effected at temperatures lower than this crystalization temperature. Otherwise, amorphous alloys would lose their required magnetic properties. Thus, fusion bonding is more difficult to achieve in the case of amorphous alloys than in the case of Sendust. Although the use of resinous materials can be considered as a gap filling material, their pronounced characteristic in thermal expansion and contraction renders them unsuitable for such applications where the gap length is required to meet the tolerance range of .+-.0.1 micrometers.